1. Field of Invention
The present invention relates to a test method of an electro-optical device, a test circuit of the electro-optical device, the electro-optical device, and electronic equipment.
2. Description of Related Art
Electro-optical devices, such as liquid-crystal devices, are currently being widely used as display devices for many diverse types of electronic equipment. An electro-optical device of this sort typically includes an element substrate having a plurality of scanning lines and a plurality of data lines formed thereon, a counter substrate facing the element substrate, an electro-optical material sandwiched between the two substrates, and pixels, each pixel being arranged at an intersection of each of the scanning lines and each of the data lines.
It is extremely difficult to completely remove an open circuit or a short circuit of wirings of the scanning line or the data line, and defects in a pixel or a switching element (hereinafter collectively referred to as a xe2x80x9cdefectxe2x80x9d) in a manufacturing process of the electro-optical device. A certain number of defects inevitably occur. Manufactured electro-optical devices thus must be tested for the presence or absence of any defect. In a known test method, for example, a test pattern, displayed on an electro-optical device to be tested, is observed with a user""s naked eyes or by using a CCD camera to determine whether each pixel lights normally.
When the area of each pixel is very small, such as on a high-definition display, it is difficult to precisely recognize each of the pixels with a user""s naked eyes or by using a CCD camera. When a defect in a pixel causes a difference between a voltage supplied to the pixel and an intended voltage, a density difference on the screen due to the voltage difference is difficult to recognize. Such a defect in the pixel cannot be easily found. The conventional test method is thus subject to an accuracy limit.
The present invention addresses the above problem, and it is an object of the present invention to provide a test method and test circuit of an electro-optical device, the electro-optical device, and electronic equipment that enables wirings and electrodes to be accurately tested to check for the presence or absence of defects therewithin.
To address the above problem, a test method is provided to test an electro-optical device using a test circuit which operates in response to an action command signal periodically changing the level thereof. The electro-optical device includes a pixel electrode which is arranged at an intersection of each of scanning lines and each of data lines and serves as one electrode of a capacitor, and a pixel switching element connected between the pixel electrode and the data line. The test method includes a first step of supplying the pixel electrode with a data signal by turning on the pixel switching element, a second step of turning on a test switching element at a timing delayed from a timing of a level change of the action command signal in the course of outputting a voltage supplied to the pixel electrode to a reading signal-line by using the test circuit, and a third step of determining whether the voltage output to the reading signal-line corresponds to a voltage responsive to the data signal supplied to the pixel electrode.
Since the test method feeds the voltage applied to the pixel electrode to the reading signal-line and determines whether the fed voltage corresponds to the voltage responsive to the data signal supplied to the pixel electrode, the presence or absence of a defect in any of the pixel electrode, a pixel switching element, a scanning line and a data line in the electro-optical device is correctly detected. Even when a noise, occurring in response to a change in level of the action command signal, is superimposed on the voltage supplied to the reading signal-line, the voltage actually supplied to the pixel electrode is accurately detected because the timing of turning on the test switching element is different from the timing of the level change of the action command signal. Accurate testing is performed without being influenced by the noise.
To address the above-referenced problem, a test circuit is provided to test an electro-optical device including a pixel electrode which serves as one electrode of a capacitor and is arranged at an intersection of each of scanning lines and each of data lines, and a pixel switching element connected between the pixel electrode and the data line. The test circuit outputs a voltage, supplied to the pixel electrode, to a reading signal-line after supplying the data signal to the pixel electrode by turning on the pixel switching element, in order to determine whether the voltage supplied to the pixel electrode corresponds to a voltage responsive to the data signal. The test circuit includes a test switching element connected between the data line and the reading signal-line, and a control circuit which operates in response to the action command signal periodically changing the level thereof, and which turns on the test switching element at a timing delayed from a timing of a level change of the action command signal.
Since the test circuit determines whether the voltage fed to the reading signal-line corresponds to the voltage responsive to the data signal supplied to the pixel electrode, the presence or absence of a defect in the electro-optical device is correctly detected in the same way as described in connection with the above-referenced test method. Furthermore, even when a noise takes place at the timing of the level change of the action command signal, the test circuit accurately detects the voltage supplied to the pixel electrode because the timing of outputting the voltage, supplied to the pixel electrode, to the reading signal-line is different from the timing of the level change of the action command signal. The use of the test circuit enables testing to be accurately performed without being influenced by the noise. The test circuit may be arranged on the substrate of the electro-optical device, as part of the electro-optical device, or may be a device that is separate from the electro-optical device.
Preferably, in the test circuit, the control circuit turns on the test switching element at a timing delayed from the timing of the level change of the action command signal by a duration of time falling within a range from one-eighth to one-quarter the period of the action command signal. When the timing of turning on the test switching element is delayed by a duration of time equal to half the period of the action command signal, the noise is superimposed on the voltage supplied to the reading signal-line, and the voltage supplied to the pixel electrode is not accurately detected. The noise has a predetermined width along the time axis. In view of these points, the timing of turning on the test switching element is preferably set to be within the above-mentioned range to exclude the effect of the noise and to accurately detect the voltage supplied to the pixel electrode.
In the test circuit, an input terminal that inputs the action command signal to the control circuit and an output terminal of the reading signal-line are preferably arranged on opposed ends of the control circuit. This arrangement shortens a portion of the reading signal-line routed out toward the input terminal, thereby reducing noise that is caused by a capacitive coupling between the reading signal-line and the wiring that feeds the action command signal.
The control circuit preferably includes an output device that outputs a control signal that changes the level thereof in response to the action command signal, and a timing modification device that delays the timing of the level change of the control signal from the timing of the level change of the action command signal. The output device can be a shift register operating in response to a clock signal as the action command signal, or an address decoder operating in response to an address signal as the action command signal. The timing modification device can be a delay device that delays the control signal, for example.
To address the previously mentioned problem, a test circuit is provided that tests an electro-optical device including a pixel electrode which is arranged at an intersection of each of scanning lines and each of data lines and serves as one electrode of a capacitor, and a pixel switching element connected between the pixel electrode and the data line. The test circuit outputs a voltage, supplied to the pixel electrode, to a reading signal-line after supplying a data signal to the pixel electrode by turning on the pixel switching element, in order to determine whether the voltage supplied to the pixel electrode corresponds to a voltage responsive to the data signal. The test circuit includes a test switching element connected between the data line and the reading signal-line, and a control circuit which turns on the test switching element in response to an action command signal periodically changing the level thereof, an input terminal that inputs the action command signal to the control circuit, and an output terminal, arranged on the end of the control circuit opposite to the input terminal, that outputs a voltage of the reading signal-line. Since the input terminal and the output terminal are arranged on opposite ends of the control circuit, the generation of noise arising from capacitive coupling is controlled.
The test circuit can be incorporated into the electro-optical device. Specifically, an electro-optical device is provided that includes a pixel electrode, arranged at an intersection of each of scanning lines and each of data lines and serving as one electrode of a capacitor, a pixel switching element connected between the pixel electrode and the data line, and a test circuit which outputs a voltage, supplied to the pixel electrode, to a reading signal-line after supplying a data signal to the pixel electrode by turning on the pixel switching element, in order to determine whether the voltage supplied to the pixel electrode corresponds to a voltage responsive to the data signal. The test circuit includes a test switching element connected between the data line and the reading signal-line, and a control circuit which operates in response to the action command signal periodically changing the level thereof, and which turns on the test switching element at a timing delayed from a timing of a level change of the action command signal.
As in the above-referenced test circuit, the control circuit in the electro-optical device may have a structure that enables the test switching element to turn on at a timing delayed from the timing of the level change of the action command signal by a duration of time falling within a range from one-eighth to one-quarter the period of the action command signal, or may have a structure which includes an input terminal that inputs the action command signal to the control circuit and an output terminal, arranged on the end of the control circuit opposite to the input terminal, that outputs a voltage of the reading signal-line. In this way, accurate testing is performed.
The capacitor in the above electro-optical device may be formed of the pixel electrode serving as one electrode, a counter electrode serving as the other electrode, and an electro-optical material sandwiched between the one electrode and the other electrode. In this case, testing is performed when an electro-optical capacitor is formed of an electro-optical material sandwiched between a pixel electrode and a counter electrode in the electro-optical device. As a capacitor that stores charge responsive to the voltage supplied to the pixel electrode, the electro-optical device may include a storage capacitor having one electrode thereof connected to the pixel electrode and the other electrode thereof connected to a capacitive line. In this arrangement, testing can be performed prior to manufacturing the electro-optical device, in other words, at a prior phase of the manufacture of the electro-optical device in which the electro-optical material is just sandwiched between the pixel electrode and the counter electrode. The form of the capacitor is not important as long as a charge that is responsive to the voltage is stored in the capacitor with the pixel electrode as one electrode thereof as a result of applying the voltage responsive to the data signal to the pixel electrode even if neither electro-optical capacitor nor storage capacitor is formed.
Electronic equipment may include the above-referenced electro-optical device. Since accurate testing is performed on the electro-optical device, the electronic equipment incorporating the electro-optical device becomes highly reliable.